1. Field of the Invention
This invention relates to endless belt conveying systems and more particularly to scraper cleaning devices used in connection therewith.
2. Description of Prior Art
Endless conveyor belts made of fabric, rubber, synethetic materials, and the like are commonly employed to convey various powdered, bulk, and aggregate materials, eg. mineral ores, chemicals, sand or coal, from an input soruce to a delivery station. A typical installation includes an endless belt trained over two rotating drums with a cleaning mechanism or scraper device located at a cleaner station intermediate the drums on the endless belt loop's return side or adjacent the belt's discharge end. The scraper device is utilized, of course, to remove any conveyed material tending to cling to the belt after discharge. A build up of such adhered material can, of course, cause belt wear and faulty belt tracking, can require extra power to drive the belt, and can effect the belt's capacity to convey material.
Various prior art belt cleaning devices have been utilized to eliminate particulate and other type materials from adhering to conveyor belts, but these devices have met with limited success. A common prior art scraper cleaner comprised a series of blades -- sometimes angled relative to the direction of belt travel and other times aligned in one or more rows transversely thereof -- rigidly carried by an elongate support member which itself was biased by counterbalancing weights or springs to effect scraping engagement of the entire series of blades as a unit against the conveyor belt. Another similar prior art device included a single blade mounted substantially transversely of the belt and rigidly supported by a carrier which itself was biased towards the belt at its two ends by a coil spring and shaft type of biasing member.
However, because of the type of biasing used, neither of these prior art devices provided means for continuously assuring scraping engagement across the conveyor belt's operating surface, viz. any local immovable obstruction on the belt would bias the rigidly supported blade or blade series away from the belt. Additionally, if the belt had localized wear areas occurring on its surface, no scraping of the worn areas would occur as the prior art devices provided no localized biasing of any individual scraper element or even of the series of scraper members.
Another problem encountered with utilization of cleaning devices of the prior art is that occasionally a conveyor belt will inadvertently reverse, such as during a power failure or when the conveyor belt drive system's safety brakes fail. This is especially prevalent when the belt is operating on a steep incline and a massive weight of conveyed material is on the belt. Two problems arise then with an unexpected belt reversal; these are due primarily to the tendency of the prior art devices to continuously bias the scraper elements against the belt. First, damage could occur to the belt itself in the form of a rip in the belt's splice if the splice is forcibly dragged in a reverse direction back past the cleaner's blades. Secondly, the prior art cleaner device itself could be damaged, as they were typically designed to function and withstand forces in the normal operating direction only.
Yet another problem associated with prior art belt cleaning devices is the fact that the majority of them had to be mounted adjacent a tightened portion of the belt where vertical belt movement was limited, such as near a belt's delivery drum on the return belt portion, or near a belt's so-called snub drum.
Examples of the prior art typifying the foregoing problems are illustrated in U.S. Pat. Nos. 1,875,442; 3,315,794; and 3,999,649.